The present invention relates to an ultrasound diagnostic apparatus for displaying an elasticity image expressing hardness or softness of a living tissue in a subject and a control program of the same.
An ultrasound diagnostic apparatus for synthesizing an elasticity image expressing hardness or softness of a living tissue in a subject and a B-mode image and displaying a resultant image is disclosed in, for example, Japanese Unexamined Patent Application Publication No. 2007-282932. For example, the elasticity image is generated as follows. First, a physical quantity related to elasticity of a subject is calculated on the basis of an echo signal obtained by transmitting an ultrasound wave to the subject. On the basis of the calculated physical quantity, an elasticity image made of a color according to the elasticity is generated and displayed.
The physical quantity related to elasticity is, for example, a strain. In Japanese Unexamined Patent Application Publication No. 2008-126079, a method of estimating a strain in a sound ray direction of ultrasound wave is disclosed.
In recent years, it may be desirable to evaluate a liver disease by an ultrasound diagnostic apparatus capable of displaying an elasticity image. Generation of an elasticity image by using a strain in a liver which occurs due to pulsation of the heart and blood vessels may be examined. In this case, since a strain caused by pulsation is used, a strain is not always caused, and there is also a frame having no effective strain information. To display a stable elasticity image, display of an elasticity image using data of an amount of a plurality of frames within a period in which pulsation occurs a plurality of times may be examined.
Also by elements other than pulsation such as breathing and motion of a subject (body motion), the liver is deformed and a strain occurs. However, the direction of the strain is not constant as compared with the case of pulsation. In the case of forming an image of a strain in the sound ray direction, there is a case that an elasticity image in which elasticity of a living tissue is accurately reflected cannot be obtained. To eliminate the influence of breathing and a body motion, it is desirable to conduct a test in a state where the subject holds his/her breath and does not move.
However, to obtain data of an amount of a plurality of frames in a period in which heartbeat occurs a plurality of times, time of a certain degree is necessary. There is also a case where it is difficult for the subject to hold his/her breath and stay still during the time. There is, consequently, a case that a cause of preventing acquisition of a physical amount in which elasticity of a living tissue is reflected more accurately such as breathing or body motion occurs while data of an amount of a plurality of frames is obtained, and it is difficult to acquire an elasticity image in which the elasticity of the living tissue is reflected more accurately.